Mechanisms for forming FinFET device

ABSTRACT

Embodiments of mechanisms for forming a semiconductor device are provided. The semiconductor device includes a substrate. The semiconductor device also includes a first fin and a second fin over the substrate. The semiconductor device further includes a first gate electrode and a second gate electrode traversing over the first fin and the second fin, respectively. In addition, the semiconductor device includes a gate dielectric layer between the first fin and the first gate electrode and between the second fin and the second gate electrode. Further, the semiconductor device includes a dummy gate electrode over the substrate, and the dummy gate electrode is between the first gate electrode and the second gate electrode. An upper portion of the dummy gate electrode is wider than a lower portion of the dummy gate electrode.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. application Ser. No. 15/986,549, filed May 22, 2018, which is a divisional of U.S. application Ser. No. 14/067,424, filed on Oct. 30, 2013 and entitled “Mechanisms for Forming FINFET Device,” now U.S. Pat. No. 9,991,285 issued on Jun. 5, 2018, which applications are hereby incorporated herein by reference in their entireties.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications, such as personal computers, cell phones, digital cameras, and other electronic equipment. The semiconductor devices are fabricated by sequentially depositing insulating or dielectric layers, conductive layers, and semiconductor layers over a semiconductor substrate, and patterning the various material layers using lithography and etching processes to form circuit components and elements on the semiconductor substrate.

As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues have resulted in the development of three-dimensional designs, such as a fin field effect transistor (FinFET). The FinFET is fabricated with a thin vertical “fin” (or fin structure) extending from a substrate. The channel of the FinFET is formed in this vertical fin. A gate is provided over the fin. Advantages of the FinFET may include reducing the short channel effect and higher current flow.

However, since the feature sizes continue to decrease, fabrication processes continue to become more difficult to perform. Therefore, it is a challenge to form a reliable semiconductor device including the FinFET.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the embodiments, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings.

FIG. 1 is a perspective view of a fin field effect transistor (FinFET) device, in accordance with some embodiments.

FIG. 2A is a top view showing the layout of a semiconductor device that includes two or more FinFET devices, in accordance with some embodiments.

FIG. 2B is a cross-sectional view of the semiconductor device taken along the line b-b of FIG. 2A, in accordance with some embodiments.

FIG. 2C is a cross-sectional view of the semiconductor device taken along the line c-c of FIG. 2A, in accordance with some embodiments.

FIGS. 3A-3C are top views of various stages of a process for forming a semiconductor device, in accordance with some embodiments.

FIGS. 4A-4D are cross-sectional views of various stages of a process for forming a semiconductor device, in accordance with some embodiments.

FIGS. 5A-5D are cross-sectional views of various stages of a process for forming a semiconductor device, in accordance with some embodiments.

FIGS. 6A-6B are cross-sectional views of a semiconductor device, in accordance with some embodiments.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the embodiments of the disclosure are discussed in detail below. It should be appreciated, however, that the embodiments can be embodied in a wide variety of specific contexts. The specific embodiments discussed are merely illustrative, and do not limit the scope of the disclosure.

It is to be understood that the following disclosure provides many different embodiments, or examples, for implementing different features of the disclosure. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. Moreover, the performance of a first process before a second process in the description that follows may include embodiments in which the second process is performed immediately after the first process, and may also include embodiments in which additional processes may be performed between the first and second processes. Various features may be arbitrarily drawn in different scales for the sake of simplicity and clarity. Furthermore, the formation of a first feature over or on a second feature in the description that follows include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. Some variations of the embodiments are described. Throughout the various views and illustrative embodiments, like reference numbers are used to designate like elements.

Referring to FIG. 1, illustrated is a perspective view of a fin field effect transistor (FinFET) device 100, in accordance with some embodiments. The FinFET device 100 includes a substrate 102. The substrate 102 includes a semiconductor substrate. In some embodiments, the substrate 102 is a bulk semiconductor substrate, such as a silicon wafer. The substrate 102 may be silicon in a crystalline structure. In some other embodiments, the substrate 102 includes other elementary semiconductors such as germanium, or it includes a compound semiconductor. The compound semiconductor may include silicon carbide, gallium arsenide, indium arsenide, indium phosphide, and/or the like. In some embodiments, the substrate 102 includes a semiconductor-on-insulator (SOI) substrate. The SOI substrate may be fabricated using a separation by implantation of oxygen (SIMOX) process, wafer bonding process, and/or other suitable methods.

The FinFET device 100 also includes one or more fin structures 104 (e.g., Si fins) that extend from the substrate 102. The fin structures 104 may optionally include germanium. The fin structures 104 may be formed by using suitable processes such as photolithography and etching processes. In some embodiments, the fin structures 104 are etched from the substrate 102 using dry etch or plasma processes. Isolation structures 108, such as shallow trench isolation (STI) structures, are formed to surround the fin structures 104. In some embodiments, a lower portion of the fin structure 104 is surrounded by the isolation structure 108, and an upper portion of the fin structure 104 protrudes from the isolation structure 108, as shown in FIG. 1.

The FinFET device 100 further includes a gate structure including a gate electrode no and a gate dielectric layer 106. The gate structure is formed over a central portion of the fin structures 104. In some embodiments, multiple gate structures are formed over the fin structures 104. Numerous other layers may also be present in the gate structures, for example, capping layers, interface layers, spacer elements, and/or other suitable features.

In some embodiments, the gate dielectric layer 106 includes an interfacial layer (not shown) adjacent to the fin structures 104. The interfacial layer may include silicon oxide. The gate dielectric layer 106 may include other dielectric materials, such as silicon oxide, silicon nitride, silicon oxynitride, dielectric material(s) with high dielectric constant (high-k), or combinations thereof. Examples of high-k dielectric materials include hafnium oxide, zirconium oxide, aluminum oxide, hafnium dioxide-alumina alloy, hafnium silicon oxide, hafnium silicon oxynitride, hafnium tantalum oxide, hafnium titanium oxide, hafnium zirconium oxide, the like, or combinations thereof.

The gate electrode 110 may include polysilicon or metal including materials, such as TiN, TaN.NiSi, CoSi, Mo, Cu, W, Al, Co, Zr, Pt, other suitable materials, or combinations thereof. The gate electrode 110 may be formed in a gate last process (or gate replacement process).

Each of the fin structures 104 includes a channel region 112 surrounded or wrapped by the gate electrode 110 and the gate dielectric layer 106. The fin structures 104 may be doped to provide a suitable channel for an N-type FinFET (NMOS device) or P-type FinFET (PMOS device). The fin structures 104 may be doped using a suitable process, such as an ion implantation process, diffusion process, annealing process, other applicable processes, or combinations thereof. Each of the fin structures 104 includes a source region 114 and a drain region 116 between the channel region 112. The FinFET device 100 may be a device included in a microprocessor, memory cell (e.g., SRAM), and/or other integrated circuits.

As mentioned above, a FinFET device may include multiple gate structures and multiple fins. FIG. 2A is a top view showing the layout of a semiconductor device 10 that includes two or more FinFET devices, in accordance with some embodiments. As shown in FIG. 2A, a portion of the semiconductor device 10 is illustrated. The semiconductor device 10 includes FinFET devices bow and mob. The isolation structures 108, surrounding the FinFET devices bow and mob, electrically isolate the FinFET devices bow and mob from each other.

As shown in FIG. 2A, the FinFET devices bow and mob include multiple fins and multiple gate electrodes, in accordance with some embodiments. The FinFET device bow includes multiple fins 104 a and multiple gate electrodes 110 a traversing over the fins 104 a. The fins 104 a may be substantially parallel to each other. The gate electrode 110 a may also be parallel to each other and substantially perpendicular to the fins 104 a. Similarly, the FinFET device 100 b also includes multiple fins 104 b and multiple gate electrodes 110 b.

A dummy gate electrode 110 d is between the FinFET devices 100 a and 100 b, in accordance with some embodiments. The dummy gate electrode 110 d may be used to reduce the pattern-loading effects (or iso-dense effects). The dummy gate electrode 110 d is designed to be not electrically connected to the fins 104 a and 104 b or to the gate electrodes 110 a and 110 b. As shown in FIG. 2A, each of the fins 104 a has a fin terminal 105 a near the dummy gate electrode 110 d. The dummy gate electrode 110 d is separated from the fin terminal 105 a by a spacing D. Since the integration density of electronic components continues to increase by continual reductions in minimum feature size, the spacing D between the fin terminal 105 a and the dummy gate electrode 110 d is getting smaller. In some embodiments, the length of the spacing D is in a range from about 10 nm to about 120-nm.

FIG. 2B is a cross-sectional view of the semiconductor device 10 taken along the line b-b of FIG. 2A, in accordance with some embodiments. FIG. 2C is a cross-sectional view of the semiconductor device 10 taken along the line c-c of FIG. 2A, in accordance with some embodiments. In some embodiments, the gate dielectric layer 106 and a gate electrode layer (e.g., a polysilicon layer) are sequentially deposited over the isolation structures 108 and the fins (including the fins 104 a and 104 b). Afterwards, patterned hard masks 112 a and 112 b are formed over the gate electrode layer. The gate electrode layer and the gate dielectric layer 106 are then partially removed using etching processes. As a result, a number of gate stacks are formed. The gate stacks include the gate dielectric layer 106 and the gate electrodes 110 a and 110 b. The dummy gate electrode 110 d is also formed over the isolation structure 108.

As shown in FIG. 2B, the profiles of the gate electrode 110 a and the dummy gate electrode 110 d are substantially the same in some embodiments. In some other embodiments, the profile of the gate electrode 110 a is more tapered than that of the dummy gate electrode 110 d.

However, because the spacing D is small, a residue 114 may be left between the dummy gate electrode 110 d and the fin terminal 105 a of the fin 104 a. The residue may come from the material of the gate electrode layer not being fully removed, or being re-deposited during the etching process. In some embodiments, the residue 114 is in direct contact with the dummy gate electrode 110 d and the fin 104 a. In some embodiments, the residue 114 is also formed between and in contact with the dummy gate electrode 110 d and the fin 104 b (see FIG. 2A). As a result, a short circuiting may be formed between the fins 104 a and 104 b through the dummy gate electrode 110 d and the residue 114, which leads to a reduction of yield.

As the spacing D continues to shrink, the problems mentioned above are exacerbated in some embodiments. Therefore, it is desirable to find alternative mechanisms for forming a semiconductor device having FinFET devices to reduce or resolve the problems mentioned above.

FIGS. 3A-3C are top views of various stages of a process for forming a semiconductor device 30, in accordance with some embodiments. FIGS. 4A-4D are cross-sectional views (taken along the line I-I of FIGS. 3A-3C) of various stages of a process for forming the semiconductor device 30, in accordance with some embodiments. FIGS. 5A-5D are cross-sectional views (taken along the line J-J of FIGS. 3B-3C) of various stages of a process for forming the semiconductor device 30, in accordance with some embodiments.

As shown in FIGS. 3A and 4A, the fins 104 a and 104 b are formed over the substrate 102, in accordance with some embodiments. In some embodiments, the substrate 102 is etched to form the fins 104 a and 104 b by first depositing and patterning a hard mask layer (not shown) on the substrate 102. The hard mask layer forms a pattern covering a portion of the substrate 102. Afterwards, the substrate 102 is etched to form trenches between the regions covered by the hard mask layer. As a result, the fins 104 a and 104 b are formed between the trenches.

The trenches are formed into the isolation structures 108 to surround the fins 104 a and 104 b, as shown in FIGS. 3A and 4A in accordance with some embodiments. A dielectric material (e.g., silicon oxide) is deposited into the trenches and covers the fins 104 a and 104 b. Afterwards, the dielectric material is planarized down to the top surfaces of the fins or the hard mask layer, and then the dielectric material is etched to a level below the top surfaces of the fins 104 a and 104 b. As a result, upper portions of the fins 104 a and 104 b protrude above the isolation structures 108, and lower portions of the fins 104 a and 104 b are surrounded and covered by the isolation structures 108, as shown in FIG. 4A.

Alternatively, the isolation structures 108 are formed first over the substrate 102. Trenches between the isolation structures 108 are formed to expose the substrate 102. A semiconductor material, such as silicon, silicon germanium, or other applicable materials, is then grown in the trenches to form the fins 104 a and 104 b by using, for example, an epitaxial process. After the fins 104 a and 104 b are grown to have the desired height, the isolation structures 108 are etched down to a level below the top surfaces of the fins 104 a and 104 b. As a result, portions of the fins 104 a and 104 b protrude above the isolation structures 108, as shown in FIG. 4A.

Referring to FIGS. 3B and 5A, the gate dielectric layer 106 and a gate electrode layer 310 are formed over the fins 104 a and 104 b and the isolation structures 108, in accordance with some embodiments. The gate electrode layer 310 may be made of polysilicon in some embodiments. The gate electrode layer 310 may be deposited using a CVD process or other applicable processes.

The gate electrode layer 310 and the gate dielectric layer 106 are to be patterned to form gate stacks traversing over the fins 104 a and 104 b. As shown in FIGS. 4B and 5B, one or more hard masks are formed over the gate electrode layer 310, in accordance with some embodiments. In some embodiments, stacks of hard masks 112 a and 112 b are formed over the gate electrode layer 310. The hard mask 112 a may be made of silicon oxide, silicon nitride, silicon oxynitride, or other applicable materials. The hard mask 112 b may be made of silicon oxide, silicon nitride, silicon oxynitride, or other applicable materials. The hard masks 112 a and 112 b form a pattern covering a portion of the gate electrode layer 310 to facilitate a subsequent patterning process for forming gate electrodes.

Multiple etching operations are performed to etch the gate electrode layer 310 to form the gate electrodes, in accordance with some embodiments. As shown in FIGS. 4C and 5C, a first etching operation is performed to remove an upper portion of the gate electrode layer 310, in accordance with some embodiments. The upper portion of the gate electrode layer 310 may be above the fins 104 a and 104 b. For example, the gate electrode layer 310 is partially etched until the gate dielectric layer 106 above the top surfaces of the fins 104 a and 104 b is exposed.

The first etching operation may be performed in a process chamber. In some embodiments, the etchant used in the first etching operation includes Cl₂, SF₆, N₂, CF₄, CHF₃, CH₂F₂, N₂H₂, O₂, He, other suitable etchants, or combinations thereof. The pressure of the process chamber may be maintained in a range from about 1 mtorr to about 40 mtorr. The temperature of the first etching operation may be maintained at a temperature ranging from about 10 degrees C. to about 50 degrees C. The power of bias used in the first etching operation may be in a range from about 100 W to about 1000 W.

As shown in FIGS. 3C, 4D, and 5D, a second etching operation is performed to partially remove a lower portion of the gate electrode layer 310 to form gate electrodes 310 a and 310 b, and a dummy gate electrode 310 d, in accordance with some embodiments. In some embodiments, the second etching operation and the first etching operation are performed in the same process chamber. The process chamber may be vacuumized to remove the etchant used in the first etching operation before the second etching operation is performed. In some embodiments, a voltage bias is applied to the substrate 102. Therefore, the etchant used in the second etching operation may be attracted to mainly etch the lower portion of the gate electrode layer 310. The upper portion of the gate electrode layer 310 substantially maintains the profile which has been formed in the first etching operation. As a result, the gate electrodes 310 a and 310 b and the dummy gate electrode 310 d are formed.

In some embodiments, the etchant used in the second etching operation includes Cl₂, BCl₃, N₂, CF₄, CHF₃, CH₂F₂, N₂H₂, O₂, other suitable etchants, or combinations thereof. The pressure of the process chamber may be maintained in a range from about 1 mtorr to about 10 mtorr. The temperature of the second etching operation may be maintained at a temperature ranging from about 10 degrees C. to about 50 degrees C. The power of bias used in the second etching operation may be in a range from about 100 W to about 1000 W.

In the second etching operation, process parameters are adjusted to control the profile of the dummy gate electrode 310 d. In some embodiments, various etchants are used in combination in the second etching operation. For example, Cl₂ is used as a first etchant, and CHF₃ and/or CH₂F₂ are/is used as a second etchant. In some embodiments, by tuning the ratio of the amount of the first etchant to the second etchant, the profile of the dummy gate electrode 310 d is controlled. For example, by raising the component of the first etchant, the lateral etching rate may be increased. As a result, the bottom portion of the dummy gate electrode 310 d may be more recessed. Other process parameters may also be adjusted to control the profile of the dummy gate electrode 310 d.

As shown in FIGS. 4D and 5D, a recess 314 is formed at a lower portion of the dummy gate electrode 310 d, in accordance with some embodiments. The recess 314 extends from a sidewall 316 of an upper portion of the dummy gate electrode 310 d. That is, the dummy gate electrode 310 d is recessed at a lower portion of the dummy gate electrode 310 d. As shown in FIGS. 4D and 5D, the dummy gate electrode 310 d has a width W₁ near the top 312 of the dummy gate electrode 310 d. The dummy gate electrode 310 d also has a width W₃ near the substrate 102. The width W₂ of the dummy gate electrode 310 d is between the widths W₁ and W₃. The width W₁ is larger than the width W₃.

The width W₁ may be in a range from about 10 nm to about 40 nm. The width W₃ may be in a range from about 5 nm to about 30 nm. In some embodiments, the ratio of the width W₃ to the width W₁ (W₃/W₁) is in a range from about ⅛ to about 3. In some embodiments, the width W₂ is larger than the width W₃ and smaller than the width W₁. In some embodiments, the width W₂ is substantially equal to the width W₃. In some embodiments, the lower portion of the dummy gate electrode 310 d has a vertical sidewall 317. The sidewall 317 may be substantially parallel to the sidewall 316 of the upper portion of the dummy gate electrode 310 d. In some other embodiments, the sidewall 317 has a curved surface.

As shown in FIG. 4D, the dummy gate electrode 310 d shrinks at the lower portion. The spacing D′ between the fin terminal 105 a of one of the fins 104 a and the sidewall 317 of the dummy gate electrode 310 d is enlarged when compared to the spacing D of the structure shown in FIG. 2C. In some embodiments, the length of the spacing D′ is in a range from about from about 10 nm to about 120 nm. Because the spacing D′ is larger, there is less residue formed between the dummy gate electrode 310 d and the fin terminal 105 a of the fin 104 a. Short circuiting formed between the fin 104 a and the dummy gate electrode 310 d is significantly reduced or prevented. Similarly, the spacing between the dummy gate electrode 310 d and a fin terminal 105 b of the fin 104 b is also enlarged. Short circuiting formed between the fin 104 b and the dummy gate electrode 310 d is also significantly reduced or prevented. Therefore, the likelihood of short circuiting between the fins 104 a and 104 b through the dummy gate electrode 310 d is reduced, compared with the embodiments illustrated in FIG. 2C.

As shown in FIG. 5D, the gate electrodes 310 a and the 310 b have vertical sidewalls in some embodiments. There may be no recess formed at the sidewalls of the gate electrodes 310 a and 310 b. Embodiments of the disclosure are not limited thereto. In some other embodiments, the gate electrodes 310 a and 310 b have inclined sidewalls. In some embodiments, the bottom profile (the profile of the lower portion) of the dummy gate electrode 310 d is more recessed than that of the gate electrode 310 a or 310 b.

As shown in FIGS. 4D and 5D, the portion of the gate dielectric layer 106 not covered by the gate electrodes 310 a and 310 b and the dummy gate electrode 310 d is removed, in accordance with some embodiments. An etching process may be performed to partially remove the gate dielectric layer 106 so as to expose a portion of the fins 104 a and 104 b.

Some processes may then be performed to finish the formation of the semiconductor device 30. For example, various processes may be performed to form FinFET devices 300 a and 300 b of the semiconductor device 30, as shown in FIG. 3C in accordance with some embodiments.

In some embodiments, the fins 104 a and 104 b not under the gate structure are then doped to form lightly doped drain and source (LDD) regions (not shown). The dopant used depends on the conductivity type of the transistor. The LDD regions may be doped by 10 n-implantation or by plasma doping where dopants are deposited onto and into the fins 104 a and 104 b and annealed. Source and drain (S/D) regions (not shown) may also be formed across the gate electrodes 310 a and 310 b over and between the fins 104 a and 104 b, similar to the structure shown in FIG. 1. The S/D regions may be formed by an ion-implantation process. Alternatively, a portion of the fins 104 a and 104 b may be removed and epitaxially re-growing the removed portion under doping condition to form the S/D regions.

In some embodiments, a gate replacement process (or a gate last process) is performed to replace the polysilicon of the gate electrodes 310 a and 310 b with a metal material, which includes a work function material. In these cases, the gate electrodes 310 a and 310 b include one or more metal materials. The dummy gate electrode 310 d may also be replaced with the metal material. Therefore, the dummy gate electrode 310 d may also include one or more metal materials.

As mentioned above, the profiles of the gate electrodes and the dummy gate electrode may be tuned by adjusting the etching process conditions. FIGS. 6A-6B are cross-sectional views of a semiconductor device 30′ similar to the structure shown in FIGS. 4D and 5D, in accordance with some embodiments.

As shown in FIG. 6A, the semiconductor device 30′ includes gate electrodes 310 a′ and 310 b′ traversing over the fins 104 a and 104 b. A dummy gate electrode 310 d′ is between the gate electrodes 310 a′ and 310 b′ in some embodiments. The dummy gate electrode 310 d′ is also between the fins 104 a and 104 b.

As mentioned above, in the second etching operation, Cl₂ is used as a first etchant, and CHF₃ and/or CH₂F₂ are/is used as a second etchant, in accordance with some embodiments. In some embodiments, more amount of the second etchant is used when compared with the embodiments illustrated in FIG. 4D. As a result, the profile shown in FIG. 6A may be obtained. The lower portion of the dummy gate electrode 310 d′ has an inclined sidewall 317′, and the upper portion of the dummy gate electrode 310 d′ has a substantially vertical sidewall 316′. A recess 314′ is formed from the sidewall 316′ and extends inwardly to the center of the dummy gate electrode 310 d′.

As shown in FIG. 6A, the dummy gate electrode 310 d′ gradually shrinks at the lower portion, in accordance with some embodiments. The width W₂′ of the dummy gate electrode 310 d′ is gradually reduced to be the width W₃′ at the bottom portion. Therefore, the spacing D″ between the fin terminal 105 a of one of the fins 104 a and the sidewall 317′ of the dummy gate electrode 310 d′ is enlarged when compared to the spacing D of the structure shown in FIG. 2C. Therefore, the likelihood of short circuiting between the fins 104 a and 104 b through the dummy gate electrode 310 d′ is reduced, compared with the structure shown in FIG. 2C.

As shown in FIG. 6B, the lower portion of the gate electrode 310 a′ has an inclined sidewall 319, in accordance with some embodiments. In some embodiments, the width W₄ of the gate electrode 310 a′ gradually increased to be the width W₅ at the bottom portion. The width W₅ is wider than the width W₃′ of the dummy gate electrode 310 d′. There is an angle θ₁ between the inclined sidewall 319 and an extending plane of the bottom of the gate electrode 310 a′. The angle θ₁ is larger than about 90 degrees in some embodiments. There is an angle θ₂ between the sidewall 317′ and an extending plane of the bottom of the dummy gate electrode 310 d′. The angle θ₂ is less than the angle θ₁ and no more than about 90 degrees in some embodiments. In some other embodiments, the angle θ₁ is less than 90 degrees. In these cases, the angle θ₂ is still less than the angle θ₁ in some embodiments. In some embodiments, the angle θ₁ is larger than the angle θ₂ by an angle difference (θ₁−θ₂) ranging from about 0.1 degrees to about 90 degrees. In some other embodiments, the angle θ₁ and the angle θ₂ are the same.

Embodiments of the disclosure have many variations. For example, the sidewalls 317′ and/or 319 are not limited to be planar planes. In some other embodiments, one or all of the sidewalls 317′ and 319 has a curved surface.

Embodiments of mechanisms for forming a semiconductor device including FinFET devices are provided. By performing an etching process including multiple etching operations to a gate electrode layer, gate electrodes traversing over fins and one or more dummy gate electrodes between the fins are formed. The etching operation is tuned to control the profile of the lower portion of the dummy gate electrode. The dummy gate electrode shrinks at the lower portion. A recess is formed at the lower portion of the dummy gate electrode. Therefore, the distance between the terminals of the fins and the bottom of the dummy gate electrode is enlarged. Short circuiting between the fins and the dummy gate electrode is reduced or prevented. The yield and the reliability of the semiconductor device are therefore improved.

In accordance with some embodiments, a semiconductor device is provided. The semiconductor device includes a substrate. The semiconductor device also includes a first fin and a second fin over the substrate. The semiconductor device further includes a first gate electrode and a second gate electrode traversing over the first fin and the second fin, respectively. In addition, the semiconductor device includes a gate dielectric layer between the first fin and the first gate electrode and between the second fin and the second gate electrode. Further, the semiconductor device includes a dummy gate electrode over the substrate, and the dummy gate electrode is between the first gate electrode and the second gate electrode. An upper portion of the dummy gate electrode is wider than a lower portion of the dummy gate electrode.

In accordance with some embodiments, a semiconductor device is provided. The semiconductor device includes a substrate. The semiconductor device also includes a first fin and a second fin over the substrate. The semiconductor device further includes a first gate electrode and a second gate electrode traversing over the first fin and the second fin, respectively. In addition, the semiconductor device includes a gate dielectric layer between the first fin and the first gate electrode and between the second fin and the second gate electrode. Further, the semiconductor device includes a dummy gate electrode over the substrate, and the dummy gate is between the first fin and the second fin. A recess is at a lower portion of the dummy gate electrode.

In accordance with some embodiments, a method for forming a semiconductor device is provided. The method includes forming a first fin and a second fin over a substrate and depositing a gate dielectric layer and a gate electrode layer over the first fin, the second fin, and the substrate. The method also includes performing an etching process to partially remove the gate electrode layer such that a first gate electrode and a second gate electrode are formed to respectively traverse over the first fin and the second fin. A dummy gate electrode is also formed over the substrate and between the first fin and the second fin, and a bottom portion of the dummy gate electrode is recessed.

Although the embodiments and their advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the embodiments as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods, and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed, that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the disclosure. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. In addition, each claim constitutes a separate embodiment, and the combination of various claims and embodiments are within the scope of the disclosure. 

What is claimed is:
 1. A method for forming a semiconductor device, the method comprising: forming a first fin and a second fin; forming an isolation region between the first fin and the second fin; forming a gate dielectric layer over the first fin, the second fin, and the isolation region; forming a gate electrode layer over the gate dielectric layer; performing a first etching process, wherein the first etching process partially removes an upper portion of the gate electrode layer to form an upper portion of a first gate electrode over the first fin, an upper portion of a second gate electrode over the second fin, and an upper portion of a dummy gate electrode over the isolation region; and performing a second etching process after the first etching process, wherein the second etching process partially removes a lower portion of the gate electrode layer to form the first gate electrode, the second gate electrode, and the dummy gate electrode, wherein after the second etching process, the upper portion of the dummy gate electrode has a first width, a lower portion of the dummy gate electrode has a second width, the upper portion of the first gate electrode has a third width, and a lower portion of the first gate electrode has a fourth width, wherein the first width is larger than the second width, and the third width is smaller than the fourth width.
 2. The method of claim 1, further comprising stopping the first etching process when the gate dielectric layer over an upper surface of the first fin and over an upper surface of the second fin is exposed while the gate dielectric layer over the isolation region is covered by a lower portion of the gate electrode layer, wherein the second etching process is performed after stopping the first etching process.
 3. The method of claim 1, wherein the first etching process and the second etching process are performed using different etchants.
 4. The method of claim 3, wherein an etchant used in the first etching process comprises Cl₂, SF₆, N₂, CF₄, CHF₃, CH₂F₂, N₂H₂, O2, He, or combinations thereof.
 5. The method of claim 4, wherein the second etching process is performed using a mixture of a first etchant and a second etchant, wherein the first etchant comprises Cl2, and the second etchant comprises CHF₃, CH₂F₂, or both.
 6. The method of claim 1, wherein the second etching process is performed using a mixture of a first etchant and a second etchant, wherein the method further comprises changing a ratio between the first etchant and the second etchant to modify a lateral etching rate of the second etching process.
 7. The method of claim 1, wherein the first etching process and the second etching process are performed in a same process chamber.
 8. The method of claim 7, further comprising after the first etching process and before the second etching process, removing unused portions of an etchant for the first etching process from the process chamber.
 9. The method of claim 1, wherein the second etching process forms a recess in a lower portion of the dummy gate electrode.
 10. The method of claim 1, wherein sidewalls of the upper portion of the dummy gate electrode are parallel to sidewalls of the lower portion of the dummy gate electrode.
 11. The method of claim 1, wherein sidewalls of the upper portion of the dummy gate electrode intersect with respective sidewalls of the lower portion of the dummy gate electrode.
 12. The method of claim 11, wherein the sidewalls of the lower portion of the dummy gate electrode have a linear profile.
 13. A method for forming a semiconductor device, the method comprising: forming a first fin and a second fin over a substrate; depositing a gate electrode layer over the first fin, the second fin, and the substrate; and performing an etching process, wherein the etching process partially removes the gate electrode layer to form a first gate electrode over the first fin, a second gate electrode over the second fin, and a dummy gate electrode over the substrate between the first fin and the second fin, wherein a lower portion of the dummy gate electrode is narrower than an upper portion of the dummy gate electrode, wherein a lower portion of the first gate electrode is wider than an upper portion of the first gate electrode.
 14. The method of claim 13, wherein a sidewall of a lower portion of the first gate electrode forms a first angle with a major upper surface of the substrate, and a sidewall of the lower portion of the dummy gate electrode forms a second angle with the major upper surface of the substrate, the first angle being larger than the second angle.
 15. The method of claim 14, wherein the first angle is larger than about 90 degrees, and the second angle is smaller than about 90 degrees.
 16. The method of claim 13, wherein performing the etching process comprises: performing a first etching process to partially remove an upper portion of the gate electrode layer; and after stopping the first etching process, performing a second etching process to partially remove a lower portion of the gate electrode layer, wherein the first etching process uses an etchant different from an etchant of the second etching process.
 17. A method for forming a semiconductor device, the method comprising: forming a first fin over a substrate; forming a gate electrode layer over the first fin and the substrate; performing a first etching process to remove an upper portion of the gate electrode layer disposed over an upper surface of the first fin, the first etching process forming an upper portion of a first gate electrode over the first fin and forming an upper portion of a dummy gate electrode adjacent to the first fin, the upper portion of the first gate electrode being spaced from the upper portion of the dummy gate electrode by a first distance; and performing a second etching process different from the first etching process to remove a lower portion of the gate electrode layer, the second etching process forming a lower portion of the first gate electrode and a lower portion of the dummy gate electrode, the lower portion of the first gate electrode being spaced from the lower portion of the dummy gate electrode by a second distance different from the first distance, the first distance and the second distance being measured along a direction parallel to a major upper surface of the substrate, wherein the second etching process removes portions of the gate electrode layer disposed under the upper portion of the dummy gate electrode to form a recess, wherein a first width of the lower portion of the dummy gate electrode is smaller than a second width of the upper portion of the dummy gate electrode, and wherein a third width of the lower portion of the first gate electrode is larger than a fourth width of the upper portion of the first gate electrode.
 18. The method of claim 17, wherein the second distance is larger than the first distance.
 19. The method of claim 17, wherein an etching gas used in the second etching process comprises a first etchant and a second etchant.
 20. The method of claim 19, wherein the method further comprises changing a ratio between the first etchant and the second etchant to modify a lateral etching rate of the second etching process. 